1 . Field
The disclosed concept relates generally to display units, and in particular, to display units configured to display trip information. The disclosed concept also relates to circuit interrupters including a display unit configured to display trip information.
2 . Background Information
Circuit interrupters, such as circuit breakers, are generally old and well known in the art. Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which heats and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system.
Industrial circuit breakers often use a circuit breaker frame, which houses a trip unit. See, for example, U.S. Pat. Nos. 5,910,760 and 6,144,271. The trip unit may be modular and may be replaced, in order to alter the electrical properties of the circuit breaker.
It is well known to employ trip units which utilize a microprocessor to detect various types of overcurrent trip conditions and provide various protection functions, such as, for example, a long delay trip, a short delay trip, an instantaneous trip, and/or a ground fault trip. The long delay trip function protects the load served by the protected electrical system from overloads and/or overcurrents, The short delay trip function can be used to coordinate tripping of downstream circuit breakers in a hierarchy of circuit breakers. The instantaneous trip function protects the electrical conductors to which the circuit breaker is connected from damaging overcurrent conditions, such as short circuits. As implied, the ground fault trip function protects the electrical system from faults to ground.
The earliest electronic trip unit circuit designs utilized discrete components such as transistors, resistors and capacitors.
More recently, designs, such as disclosed in U.S. Pat. Nos. 4,428,022 and 5,525,985 , have included microprocessors, which provide improved performance and flexibility. These digital systems sample the current waveforms periodically to generate a digital representation of the current. The microprocessor uses the samples to execute algorithms, which implement one or more current protection curves.
When diagnosing field issues with a circuit interrupter, the cause of the trip and other information (e.g., without limitation, each phase current and the ground current at the time of the trip) are beneficial in diagnosing the issue. it is known to employ a liquid crystal display unit in conjunction with a circuit interrupter to display the cause of trip and other information. The liquid crystal display unit employs a battery or a rechargeable battery as a secondary power source in order to maintain the display of the cause of trip and other information during a circuit interruption. This is because the circuit interrupter loses its power source during a circuit interruption. However, batteries, even rechargeable ones, have a limited lifespan and must be periodically replaced, thus adding to the maintenance cost of the known liquid crystal display unit.
There is room for improvement in circuit interrupters.
There is also room for improvement in display units for use with circuit interrupters.